Falls are one of the greatest health risk factors for elderly people. About one third of older people above the age of 65 fall at least once a year.
Many of these falls could be avoided by early identification of fall risk and the application of effective and targeted fall prevention programs.
Fall prevention trials based on strength and balance training (SBT) have shown that the risk of falling for elderly people can be reduced. Balance performance measures can be used as early indicators of fall risk, and also to measure the progress of fall prevention programs. The ‘sit-to-stand’ (STS) transfer has been identified as one important movement which can be used as a balance performance measure. Domain experts can compare the graph of the power generated during a sit-to-stand transfer for fall prevention with the ECG graph in cardiovascular disorders. In daily life, a person performs the STS transfer many times a day.
Conventionally, only clinical measurement systems (such as those including a force plate and an optical marker system) allow an accurate quantification of power during a sit-to-stand transfer. In these measurement systems, the force plate provides the vertical ground reaction force and the optical marker system provides a measure of displacement in three dimensions. The combination of both measurements is used to quantify the power during a sit-to-stand transfer.
These measurement systems have several drawbacks. Firstly, they are clinical equipment, which requires the user to attend a clinic. Preparing for and performing measurements is labor intensive (particularly if optical markers need to be attached to specific parts of the body). In addition, they only provide a snapshot of the user's balance performance, where, owing to the clinical setting, the user commonly performs above their average capability. Finally, the measurement systems involve a procedure which is quite cumbersome for the user.
WO 2010/035187 entitled “Power Measurement and Apparatus” discusses an apparatus for estimating the peak power used by a user in performing the vertical component of a movement, such as a sit-to-stand transfer, the apparatus comprising an accelerometer for attachment to a user and for measuring the acceleration experienced by a user; the apparatus further comprising a processor configured to receive the measurements of the acceleration from the accelerometer attached to the user; estimate the vertical accelerations from the received measurements; and estimate the power used from the vertical accelerations.
Existing activity monitoring technologies identify postures or movements by classifying a sequence of sensor data of tens of seconds or minutes in length. However, it is difficult to accurately detect a sit-to-stand transfer that is typically completed within 2 or 3 seconds.
Therefore, there is a need for a method and apparatus that can identify such a transfer from measurements of the movement of a user, so that the power used by the user in performing the movement can be calculated. There is also a need for a method and apparatus that can detect the onset and end of the transfer within a certain degree of accuracy in order for the power analysis to provide useful results.